1. Field of the Invention
The present invention relates to aqueous detergent compositions with elevated viscosity for use in liquid cleansing agents and as the base for shampoos, bath and shower gels, and other cosmetic formulations in which elevated viscosity is required.
2. Discussion of the Background
Such systems in the past have been based primarily on alkyl sulfates or alkyl ether sulfates with usually low degrees of ethoxylation. The viscosity can then be adjusted relatively easily by adding sodium chloride, ammonium chloride, sodium sulfate and other electrolytes, possibly in combination with fatty acid diethanolamides and/or other additives. Such formulations show satisfactory foam, and they are economical, but they have the serious drawback of generally severe skin irritation and poor tolerability in the mucous membranes of the eye, which is of considerable importance considering that they are frequently used daily. Added to this is the problem, that has become important recently, of possible toxic effects from the dioxane content of ether sulfates and the N-nitrosamine content of fatty acid amides, so that formulations free of nitrogen without using ether sulfates are desirable. The remaining alkyl sulfates are among the surfactants with the lowest skin and mucous membrane tolerability.
The search for milder surfactants that do not have the above-mentioned drawback has been in progress for some time. Surfactants have actually been found that are acceptable to the skin and mucous membranes, but, on the other hand, they have the drawback that they cannot be thickened with electrolytes, or only to a very limited extent [see: H. Meijer, Seifen-Ole-Fette-Wachse, vol. 113, 135 (1987), and H. Tesmann, Parfumerie und Kosmetik, vol. 68, 630 (1987)]. It has therefore been attempted to produce sufficiently high viscosities by substituting a milder, toxicologically more acceptable, but unfortunately only very poorly thickenable surfactant for a very limited portion of the alkyl sulfate or of the ether sulfate (see U.S. Pat. No. 3,038,862 and H. Meijer, loc. cit.). Thickening by means of water-soluble polymers is of limited suitability because of the negative effect on foam quality and the feeling on the skin.
Thus, there remains a need for thickenable detergent compositions acceptable to the skin and mucous membranes of the eye that are largely free of alkyl or alkyl ether sulfates and of surfactants containing nitrogen.